The present invention relates to tape recorders, i.e., tape drives, and more particularly to tape cartridge recorders which include means for detecting (1) whether a cartridge is present, (2) whether a cartridge is write-protected, and (3) whether or not there are position-indicating apertures in the tape inside the cartridge.
Tape cartridge recorders, particularly those used as secondary storage in computing systems, often include three sensors for detecting (1) whether a cartridge is properly loaded on the recorder (cartridge-present), (2) whether a loaded cartridge is write-protected (write-protect), and (3) position-indicating apertures in the magnetic tape contained in the cartridge. The cartridge-present sensor is actuated by a cartridge mounted on the recorder only when the cartridge is properly loaded and in ready position for data transfer. The write-protect sensor is actuated by the cartridge loaded on the recorder when a mechanical device on the cartridge is positioned to indicate that the tape may be written onto. When the write-protect sensor is not actuated, write heads of the recorder are disabled to prevent data transfer onto the tape. Finally, the aperture-detecting sensor is usually an optical assembly having a device directing light against the tape, and a light-sensitive device actuated by the directed light when apertures in the tape permit the light to pass therethrough. Usually, an aperture, or a series of apertures, is located proximate either end of the tape to signal an end-of-tape condition. Consequently, the aperture-detecting sensor upon detecting an aperture in the tape signals the computing system that an end-of-tape condition is imminent.
Usually, these three sensors are separately mounted on the recorder, albeit on a common housing, and individually adjustable with respect to one another. Consequently, this portion of the recorder assembly is labor intensive, due to the fact that each one of the three sensors must be individually adjusted to be actuated under the precise conditions desired. Further, the sensors are often interrelated so that adjustment of one sensor throws a previously adjusted sensor out of alignment. In such case, the previously adjusted sensor must be readjusted, further increasing assembly costs.
Further, the cartridge-present and write-protect sensors are generally mechanical microswitches. When considered in view of the precise tolerances required of these sensors, a microswitch has a relatively large tolerance so that even a properly aligned switch might not actuate in response to the desired parameters. Additionally, if not actuated for a period of time, these mechanical switches incur an oxide build-up which interferes with subsequent switch actuation. Although gold-plated and cross-bar switches, which have low-resistance oxides compared to conventional microswitches, are available, these switches are relatively expensive, further boosting the cost of the recorder.